1. Field of the Invention
This invention relates to tachometers, and particularly to a tachometer which will provide a DC output voltage of a sign representative of the direction of rotation of a shaft and of a magnitude proportional to shaft speed.
2. General Description of the Prior Art
Many applications require a DC signal indicative of the speed of rotation of a shaft. The most commonly employed device for this purpose is a brush-type generator which is, of course, an AC generator which provides a DC output by commutation. Alternately, the output of an AC generator is rectified by a solid state or other discrete rectification element. A third type device is disclosed in a previous patent application by the applicant, now U.S. Pat. No. 3,541,361, and in it hall effect crystal are electrically biased by windings of a permanent magnet AC generator and are magnetically biased by rotation of the permanent magnet as an armature. Of these devices, brush-type tachometers suffer from ripple-type outputs and undesired torque between brushes and commutator. Separate rectification of the output of pure AC generators is sometimes unsatisfactory because of poor linearity of the rectification devices used therewith and because of displacement error at zero speed. The applicant's previous invention solves most of the disadvantages of the other two devices, but it has been found that there are instances where higher output voltages are required than can be obtained from it.